Hafnium Filter to Make X-Ray CT Safer for Children

The Challenge: X-ray CT Medical Imaging has proven to be a very useful technique for observation of physical details inside of the human body. Unfortunately for young children, the Brenner Team of researchers at Columbia University has shown that the X-rays themselves can be dangerous. In large numbers the X-rays can create damaged cells in children that initiate a delayed form of fatal cancer, showing up at mid-life in a significant number of cases [1, 2]

The Solution: The solution to this challenge is to reduce the number of X rays used without reducing the observational capability. Historically, however, observational capability was improved by increasing the number of X-rays, increasing Contrast to Noise Ratio (C/NR), and allowing observation of smaller dimensions. The key, therefore, requires increasing contrast, and decreasing noise, while at the same time decreasing X-ray dose.

Increasing Contrast: Our Team of researchers has focused on increasing contrast. Installation of a Hafnium Filter in the exit window of the X-ray generating tube has been shown to narrow the X-ray photon energy spectrum, and thereby increase contrast, while at the same time decreasing X-ray dose by 40% to 50% [3].

Please see attachments:1) Photograph of replacing the copper with hafnium in the center of the Exit Window Filter of the X-ray generating tube. 2) Figure showing the X-ray photon energy spectrum produced when 120kVp electrons strike a tungsten anode (solid curve), and calculated to be present after “filtering” by hafnium (dashed curve). 3) Figure showing the effect of using the hafnium filter. These data were taken observing a CIRS Model M007TE-04 tissue equivalent abdominal phantom, 10-year old size, custom modified to contain 1 to 6 mm dia. axial rods, with x-ray absorption properties 2% above the background matrix.

Decreasing Noise: CT system manufacturers have focused on the challenge by making use of “digital post-imaging iterative reconstructive techniques” to reduce noise. Sufficient noise reduction has been achieved to allow the X-ray dose to be reduced by 40% to 50%, a significant industry advance.

Increasing Contrast plus Decreasing Noise - Adding the hafnium filter contrast increase technique to a system using digital post-imaging iterative reconstructive noise reduction increases C/NR still further, and is projected by computational modelling to achieve a 90% reduction in X ray dose [4], truly making X ray CT safer for children. This combination is ready for optimization and adoption by CT system manufacturers.